Information on feeding behaviour of tropical horseshoe crabs, Tachypleus gigas (M¨uller, 1785) is still scanty compared to Limulus polyphemus (Linnaeus, 1758). Foods condition such as decayed, sheltered and etc., would substantially influence the edibility of food by the T. gigas. However, horseshoe crabs might have specific behaviour to manipulate the foraged food. The aim of this paper was to investigate the feeding mechanism of T. gigas toward different feed conditions. Experiments were conducted inside a glass tank. A total of 30 males and females respectively were introduced to five different natural potential feeds, namely, gastropods (Turritella sp.), crustacean (Squilla sp.), fish (Lates calcarifer ), bivalve (Meretrix meretrix ) and polychaete (Nereis sp.). We have manipulated the condition of introduced feed based on the several potential foods conditions in nature such as sheltered (protected with shell, hard outer skin or host tube), unsheltered and decayed before introduced the feeds to the crabs. In present study, female crabs took shorter response period towards surrounding feed compared to males. Overall, they prefer to consume freshly dead feeds and would totally reject the sheltered feeds, such as, shell, hard outer skin and tube host. Male crabs have particular feeding behaviours to manipulate the edibility of the decayed feeds. Detailed experiments on the feeding mechanism of T. gigas could provide more information on their foraging activity in the wild.
Nowadays, the numbers of wild horseshoe crab harvested for study are increasing. However, general information on Tachyplues gigas satiation level, gut transit time, defecation pattern and acclimation period in captivity during holding period are still scanty. The aims of this study are to identify T. gigas food intake, gut transit time and defecation pattern during the rearing period by introducing the crabs with gastropod (Turritella sp.), crustacean (Squilla sp.) and bivalve (Meretrix meretrix ) in several feed ratios; 0.2%, 0.6%, 1.0%, 1.4%, 1.8% and 2.2% expressed of crabs’ body weight. The defecation of T. gigas was monitored for every three hours after being fed to measure their gut transit time and defecation pattern. Male crabs did not significantly eat until two weeks in captivity, while the females started to eat in the early first week after being harvested from the wild. The satiation levels of the females (gastropod: 1.8%±0.04; crustacean: 1.7%±0.08; bivalve: 1.8%±0.06) were significantly higher than the males’ (gastropod: 1.7%±0.08; crustacean: 1.4%±0.02; bivalve: 1.6%±0.05) for all feed types. Gut transit time of the males were significantly longer than the females’. Male crabs took shorter time (1±0 hr) to achieve their satiation than female crabs (2±0 hrs). This study provides useful information for T. gigas rearing activity and for designing a better rearing system.